/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.support;

import org.springframework.beans.BeanMetadataAttributeAccessor;
import org.springframework.util.Assert;

/**
 * Qualifier for resolving autowire candidates. A bean definition that
 * includes one or more such qualifiers enables fine-grained matching
 * against annotations on a field or parameter to be autowired.
 *
 * @author Mark Fisher
 * @author Juergen Hoeller
 * @since 2.5
 * @see org.springframework.beans.factory.annotation.Qualifier
 */

/**
 AutowireCandidateQualifier 是 Spring 框架中用于自动装配候选者限定的类，主要用于解决自动装配时的歧义问题。
 主要作用
 1. 自动装配限定
 当容器中存在多个相同类型的 Bean 时，AutowireCandidateQualifier 可以帮助精确匹配需要注入的 Bean。
 2. 注解匹配支持
	 提供与 @Qualifier 注解相对应的编程式配置支持，实现细粒度的自动装配控制。

 AbstractBeanDefinition beanDef = new GenericBeanDefinition();
 // 添加限定器
 beanDef.addQualifier(new AutowireCandidateQualifier("Primary"));
 beanDef.addQualifier(new AutowireCandidateQualifier("Profile", "production"));
 beanDef.addQualifier(new AutowireCandidateQualifier("DatabaseType", "main"));
 //案例1 ================================================
 AbstractBeanDefinition beanDef = new GenericBeanDefinition();
 // 添加限定器
 beanDef.addQualifier(new AutowireCandidateQualifier("Primary"));

	 // Java 配置类
	 @Configuration
	 public class AppConfig {
		 @Bean
		 @Primary  // 这会创建一个 typeName="Primary" 的限定符
		 public DataSource primaryDataSource() {
		 return new PrimaryDataSource();
		 }

		 @Bean
		 public DataSource secondaryDataSource() {
		 return new SecondaryDataSource();
		 }
	 }

	 // 使用的地方
	 @Service
	 public class UserService {
		 @Autowired
		 private DataSource dataSource; // 将注入标记为 @Primary 的 primaryDataSource
	 }


 //案例2 ================================================Java 配置类
	 AbstractBeanDefinition beanDef = new GenericBeanDefinition();
	 // 添加限定器
	 beanDef.addQualifier(new AutowireCandidateQualifier("Profile", "production"));

	 @Configuration
	 public class AppConfig {
		 @Bean
		 @Profile("production")  // 这会创建 typeName="Profile", value="production" 的限定符
		 public DataSource productionDataSource() {
			return new ProductionDataSource();
		 }

		 @Bean
		 @Profile("development")
		 public DataSource developmentDataSource() {
			return new DevelopmentDataSource();
		 }
	 }

	 // 当激活 "production" profile 时，会使用 productionDataSource
//案例3 ================================================
	 AbstractBeanDefinition beanDef = new GenericBeanDefinition();
	 // 添加限定器
	 beanDef.addQualifier(new AutowireCandidateQualifier("DatabaseType", "main"));
		 // 自定义限定符注解
	 @Target({ElementType.FIELD, ElementType.PARAMETER})
	 @Retention(RetentionPolicy.RUNTIME)
	 @Qualifier
	 public @interface DatabaseType {
		 String value();
	 }

	 // 使用自定义限定符
	 @DatabaseType("main")
	 public class MainDataSource implements DataSource { ... }

	 @DatabaseType("backup")
	 public class BackupDataSource implements DataSource { ... }

	 // 注入时指定使用哪个
	 @Service
	 public class DataService {
	 @Autowired
	 @DatabaseType("main")
	 private DataSource dataSource; // 将匹配 typeName="DatabaseType", value="main" 的限定符
	 }

 */
@SuppressWarnings("serial")
public class AutowireCandidateQualifier extends BeanMetadataAttributeAccessor {

	/**
	 * The name of the key used to store the value.
	 */
	//存储注解 value 属性值的键名
	public static final String VALUE_KEY = "value";

	//存储限定注解的类型名称
	private final String typeName;


	/**
	 * Construct a qualifier to match against an annotation of the
	 * given type.
	 * @param type the annotation type
	 */
	public AutowireCandidateQualifier(Class<?> type) {
		this(type.getName());
	}

	/**
	 * Construct a qualifier to match against an annotation of the
	 * given type name.
	 * <p>The type name may match the fully-qualified class name of
	 * the annotation or the short class name (without the package).
	 * @param typeName the name of the annotation type
	 */
	public AutowireCandidateQualifier(String typeName) {
		Assert.notNull(typeName, "Type name must not be null");
		this.typeName = typeName;
	}

	/**
	 * Construct a qualifier to match against an annotation of the
	 * given type whose {@code value} attribute also matches
	 * the specified value.
	 * @param type the annotation type
	 * @param value the annotation value to match
	 */
	public AutowireCandidateQualifier(Class<?> type, Object value) {
		this(type.getName(), value);
	}

	/**
	 * Construct a qualifier to match against an annotation of the
	 * given type name whose {@code value} attribute also matches
	 * the specified value.
	 * <p>The type name may match the fully-qualified class name of
	 * the annotation or the short class name (without the package).
	 * @param typeName the name of the annotation type
	 * @param value the annotation value to match
	 */
	public AutowireCandidateQualifier(String typeName, Object value) {
		Assert.notNull(typeName, "Type name must not be null");
		this.typeName = typeName;
		setAttribute(VALUE_KEY, value);
	}


	/**
	 * Retrieve the type name. This value will be the same as the
	 * type name provided to the constructor or the fully-qualified
	 * class name if a Class instance was provided to the constructor.
	 */
	public String getTypeName() {
		return this.typeName;
	}

}
